Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard. Recently, LTE-advanced (LTE-A) based on 3GPP TS release 10 supporting multiple carriers is under standardization.
Multiple carriers are supported starting from 3GPP LTE-A, and such a technique is called a carrier aggregation. One carrier corresponds to one cell, and as a result, a user equipment can receive a service from a plurality of serving cells in a multiple-carrier system.
A random access procedure is used to maintain an uplink time alignment between a base station and a user equipment or to deliver a scheduling request. In general, the random access procedure includes transmission of a random access preamble and reception of a random access response.
It has been conventionally considered that the random access procedure is performed only in one cell. However, with the introduction of a plurality of serving cells, there is a need to design a random access procedure performed in the plurality of serving cells.